Well… EACH AND EVERY STAR in the galaxy
and in the collection of galaxies making up the
known Universe (or Cosmos, a word I prefer because
it sounds cooler) goes through a life. Just
like a human being, this life cycle can be thought
of as a BIRTH stage, a NORMAL LIFE time
stage (for humans its birth till death) and
then for stars an END stage.

Now just for some background, in OUR
galaxy, the MILKY WAY Galaxy, there
are about 300,000,000,000 (three hundred
billion) stars. In the cosmos there are about
1 trillion ( 1,000,000,000,000) galaxies.
So this means there are about
3,000,000,000,000,000,000,000 STARS in the
known Cosmos. That is a very large number!

At any rate, EACH star has its own star
life, a normal lifetime shining away at a
constant rate for a period of time that depends
on the mass of the Star. For the SUN this
period is about 10 billion years. As the Sun is
about 5 billion years old, this means that the Sun
will continue to live for about another 5 billion
years. At that time, because its fuel of
hydrogen in its core will be used up, the Sun
will begin fusing Helium… when it does that
it will swell up and become a RED GIANT
star; the Sun's radius will extend out almost
to the location of MARS easily swallowing up
the EARTH. After the RED GIANT STAGE, the Sun
will stop nuclear reactions and slowly cool down
and shrink to become a WHITE DWARF star.

So the Sun will never disappear totally…
but in about 5 billion your years it will
begin its death throes and Earth will be
swallowed up.

Answer 2:

The sun is currently in its stable "mid
age", in the sense that it has "burned" (more
precisely "fused" through nuclear reaction)
half of its total hydrogen fuel. So it will
take another 5 billion years before it runs out of
hydrogen to burn. Eventually when it runs out
of hydrogen, it will expand into a "red
giant", in the sense that its size will be so
big that it will swallow Mercury, Venus, and reach
as far as the orbit of Earth. Then the sun will
shrink back into a "white dwarf".

Answer 3:

The lifespan of our sun is estimated to be
around 10 billion years. Since it began
burning about 4.6 billion years ago, this means
that this will happen in about 4.5 - 5.5 billion
years. This is due to the fact that the sun is
fueled by a fusion reaction that turns
hydrogen into helium. When this hydrogen
runs out, the sun no longer has any fuel to keep
it burning. By this time, it will have also grown
to what is called a red giant star and grown
bigger than the orbit of Earth.

Finally, all the outer layers of the sun will
be ejected off leaving behind a small, dense star
called a white dwarf, which will slowly
cool down over trillions of years. The ejected
outer layers are called a planetary nebula and
contain elements that will eventually lead to the
birth of new stars.

The sun will burn out in about five to six
billion
years, but not before becoming a red
giant and
frying if not vaporizing the Earth. When
the sun
does burn out, it will collapse to become a white
dwarf - it will still be there, but be much
smaller and much fainter.